Shroom regulates epithelial cell shape via the apical positioning of an actomyosin network

Abstract

The actin-binding protein Shroom is essential for neural tube morphogenesis in multiple vertebrate organisms, indicating its function is evolutionarily conserved. Shroom facilitates neurulation by regulating the morphology of neurepithelial cells. Shroom localizes to the apical tip of adherens junctions of neural ectoderm cells in vivo and to the apical junctional complex (AJC) in MDCK cells. Induced expression of Shroom in polarized epithelia elicits apical constriction and dramatic reorganization of the apical arrangement and packing of cells without altering apical-basal polarity. These events likely mimic the cell shape changes and cellular movements required for neurulation in vivo. The observed phenotypes depend on the ability of Shroom to alter F-actin distribution and regulate the formation of a previously uncharacterized contractile actomyosin network associated with the AJC. Targeting the C-terminal domain of Shroom to the apical plasma membrane elicits constriction and reorganization of the actomyosin network, indicting that this domain mediates Shroom's activity. In vivo, Shroom-mutant neural epithelia show a marked reduction in apically positioned myosin. Thus, Shroom likely facilitates neural tube closure by regulating cell shape changes via the apical positioning of an actomyosin network in the neurepithelium.

ZO-1- and ZO-2-Dependent Integration of Myosin-2 to Epithelial Zonula Adherens

“…A mixture of ZO1(ko)/2(kd) and ZO1(wt)/2(wt) Eph4 cells was cultured and examined by immunofluorescence microscopy ( Figure 1). In fully confluent ZO1(wt)/2(wt) Eph4 cells with linear ZO-1/2 signals at TJs, the linearly arranged signals for E-cadherin/actin/myosin-2 overlapped at the ZA, as shown previously (Bertet et al, 2004;Zallen and Wieschaus, 2004;Hildebrand, 2005). In contrast in confluent ZO1(ko)/2(kd) Eph4 cells, AJs were associated with partially linearized patterns of E-cadherin and actin, but not with myosin-2, a previously unreported AJ state, which we have designated the "prezonula-AJ."…”

Shroom4 (Kiaa1202) is an actin‐associated protein implicated in cytoskeletal organization

“…Results from our lab have shown that Shrm3 is capable of regulating cellular architecture by controlling the distribution of a contractile actomyosin network [Hildebrand, 2005]. Work presented here suggests that Shrm4 may also share this property.…”

“…Shrm4 localization is dependent on an intact actin cytoskeleton and appears to be mediated by a novel actin targeting sequence located in the central portion of the protein. Shrm4 distribution is coincident with non-muscle myosin II, suggesting that, like Shrm2 and Shrm3, Shrm4 might regulate cytoskeletal or cellular architecture through a myosin II-dependent pathway [Hildebrand, 2005;Dietz et al, 2006].…”

“…This protein family is characterized by a similar arrangement of specific motifs or active regions along their predicted linear structures. All of the Shrm-related proteins contain an Nterminal PDZ domain and a C-terminal motif, ASD2, that is capable of inducing myosin II-dependant changes in cell shape [Hildebrand, 2005;Dietz et al, 2006]. In addition, each protein has a centrally located sequence element that targets it to distinct populations of F-actin in vivo.…”

“…Work from our lab has shown that Shrm2 and Shrm3 co-distribute with myosin II in non-muscle cells and that Shrm3 requires myosin II to cause constriction [Hildebrand, 2005;Dietz et al, 2006]. Additionally, some F-actin based structures, such as stress fibers, are dependent on the activity of myosin II.…”